ZSNES is a Super Famicom (SNES) emulator written in x86 assembly. It was originally made in 1997 and was one of the most popular Super Nintendo emulators from late nineties to mid 2000s, but now is obsolete and has not been updated since 2007. Most people now just use ZSNES for its excellent netplay code.

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The ZSNES developers focused on speed over accuracy, so a hefty amount of games have bugs (and some just plain crash). The current version (v1.51) created more problems than it fixed and many problems still remain:

SNES Pseudo Hi-Res translucency on new graphics engine

Compatibility is lower than modern emulators due to low accuracy to real SNES system.

Games crashing: Der Langrisser (freezes after 2-3 hours), Super Mario RPG (freezes in many different points of the game), Star Ocean and many other games have freezing and crashing issues.

Bad sound emulation: Many games sound inaccurate on ZSNES. ZSNES's audio timer isn't floating point so there are timing artifacts in the music. ZSNES doesn't emulate release values of ADSR so held notes will sound poor.

Many of the co-processors, which are actually on the game cartridges, are emulated in strange ways. For example, Super FX is not clocked correctly; Star Fox runs twice as fast as it should.

Transparency: Kirby Dreamland 3, Mecarobot Golf, Jurassic Park and other games that use pseudo hi-res translucency won't display correctly in the default graphics engine in v1.51. To get them to display properly in v1.51, one must press 8 to switch to the old graphics engine.

Many ROM hacks and ROM hacking tools were made using ZSNES as a testing platform because of its popularity. However, because of the inaccuracies of the emulator, these tools and hacks are broken on other, more accurate emulators and real hardware.

In 2011, byuu released bZSNES - a modification of his bsnes that includes the optional inaccuracies of ZSNES and a similar GUI. This was done as an April Fools day joke. It however only has moderate compatibility with ROM hacks made specifically for ZSNES.[citation needed].